iron-oxide concretions and nodules

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This is a cluster of pyrite crystals beginning to oxidize to hematite.

This thing started out as a several pyrite crystals but is now largely oxidized to hematite.


This one is fascinating in that one side (top) has a texture like some other concretions shown here but the other side (bottom) has features that resemble meteorite regmaglypts.


West Virginia

This photo was sent to me by a fellow who found it while gardening in his yard in Kauai, Hawaii. I asked a colleague who lives in Kauai whether or not hematite concretions were found there. He said that limonite concretions did occur. Limonite is a mixed iron oxide-hydroxide. It's possible that some of the other concretions depicted here contain limonite.


This one was sent to me from Iowa. It makes a red streak and does not attract a magnet, but the specific gravity is only 4.1. Pure hematite has a specific gravity of 5.3, so this rock must contain some low-density mineral like quartz or a carbonate in addition to hematite.


I suspect that this one, from Delaware, also contains mineral phases other than hematite.

This one also looks like hematite cement holding sand grains together.

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Prepared by:

Randy L. Korotev

Department of Earth and Planetary Sciences
Washington University in St. Louis

Please don't contact me about the meteorite you think you’ve found until you read this and this.